Colored shaped aluminum article and method for manufacturing same

ABSTRACT

A shaped aluminum article has an anodized film formed on a surface, where a coloring pigment is filled in fine pores formed on the anodized film, achieving sufficient coloring.

TECHNICAL FIELD

The present invention relates to an shaped aluminum article to which color has been added, as well as a method of manufacturing such shaped aluminum article.

BACKGROUND ART

An shaped aluminum article naturally has the characteristic metallic gloss of metal aluminum, and when such shaped article is used in various applications where coloring is required, a conventional way has been to give a known surface treatment to the shaped article, as necessary, and then paint it using a pigmented paint of black, red, white or other desired color.

Besides painting as mentioned above, a method whereby the surface of an shaped aluminum article is anodized according to the sulfuric acid method or oxalic acid method, for example, and then a desired dye is impregnated or pigment is filled in the micro-fine pores formed on the surface, as well as a method whereby nickel, etc., is electrolytically deposited to add color electrolytically, are also known. However, these methods, especially the electrolytic coloring method, can add only limited colors.

In addition, the method using electrophoretic migration whereby a pigment is introduced into fine pores formed on the surface of an shaped aluminum article to add color, requires that the fine pore diameter is large enough to accommodate the pigment and that the pigment diameter is also small. With this method, however, it is difficult to add color in a stable and uniform manner, especially when adding color to a large shaped aluminum article, and it is also difficult to add a deep color because the amount of pigment that can be introduced into the fine pores is limited. Filling such pigment requires that the fine pores in the anodized film have a uniform and sufficiently large diameter, which makes it difficult to add color densely.

Also, as described in Patent Literature 1, a method, which is not a coloring method, is known which comprises: a titanyl electrolytic treatment step to anodize the surface of a shaped aluminum article beforehand and then electrolytically treat the shaped aluminum article in a mixed solution containing titanyl sulfate, etc., and complexing agent forming anions, in order to cause titanium dioxide to deposit onto the surface of the anodized film and interior surface of the fine pores, thereby forming a film containing titanium dioxide; and a sintering step to sinter this film containing titanium dioxide to change it to a photocatalytic film constituted by titanium dioxide having photocatalytic action; so that a photocatalytic film constituted by titanium dioxide is formed on the surface of the anodized film and interior surface of the fine pores.

In addition, Patent Literature 2 describes an aluminum or aluminum alloy material characterized in that it is constituted by a base material being aluminum or aluminum alloy on the surface of which an anodized film is formed, and this film is coated with a photocatalytic film produced by aggregated and deposited fine semiconductor grains of titanium oxide, etc., having photocatalytic action and an average grain size of 1 nm to 1000 nm, where a titanium oxide film is formed not in the fine pores formed on the anodized film, but outside the fine pores.

Patent Literature 3 describes applying AC voltage, in a metallic salt solution, to an aluminum material that has been anodized at high voltage to achieve electrolytic coloring, while Patent Literature 4 describes using a diluted alkaline aqueous solution to etch an aluminum material on which an anodized film has been formed and thereby chemically dissolve the exposed surface of the barrier layer at the bottom of the fine pores in the anodized film, which is followed by electrolytic coloring, or coloring by means of electrophoretic migration, in an electrolytic coloring bath containing pigment grains or metallic salt.

BACKGROUND ART LITERATURE Patent Literature

-   Patent Literature 1: Japanese Patent No. 4905659 -   Patent Literature 2: Japanese Patent No. 3326071 -   Patent Literature 3: Japanese Patent Laid-open No. Hei 11-335893 -   Patent Literature 4: Japanese Patent Laid-open No. Hei 11-236697

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

According to the prior art, where paint is applied to add color to the surface of a shaped aluminum article, the white coating film may peel or otherwise the aesthetic appearance may be reduced as the shaped aluminum article is used continuously.

Also, according to the method whereby a pigment is filled in the fine pores in the anodized film by means of electrophoretic migration, the fine pores must have a large diameter so that the pigment can be filled in them by an amount sufficient for it to demonstrate coloring strength. This can make the surface of the shaped aluminum article rough and reduce the aesthetic appearance as a result.

Furthermore, the colored film thus obtained is not a dense film; instead, the shaped aluminum article has a transparent white color because it already has some optical interference property, before titanium oxide is filled in the fine pores, due to the large diameter of the fine pores. Consequently, an opaque, white film cannot be obtained.

In addition, an attempt to achieve stable, deep coloring by means of electrophoretic migration tends to cause the pigment to deposit excessively on the surface outside the fine pores, instead of inside the fine pores, because the bath current is low during the electrophoretic migration.

Moreover, according to the method described in Patent Literature 1 above, which comprises a titanyl electrolytic treatment step to cause titanium dioxide to deposit onto the surface of the anodized film and interior surface of the fine pores and thereby form a titanium dioxide film, and a step to sinter this titanium dioxide film, it is difficult to cause a sufficient amount of photocatalytic titanium dioxide to deposit, and because the shaped aluminum article whose heat resistance is relatively poor is heated to high temperature, the shaped article may deform or its physical properties may change.

The method described in Patent Literature 2 is one whereby an anodized aluminum sheet is soaked in a titanium oxide sol to cause electrophoretic migration, so that titanium oxide grains are deposited not inside the fine pores formed on the surface of the aluminum sheet, but onto the surface, and the photocatalyst is supported as a result; however, the supported titanium oxide is used as photocatalyst; it is not supported inside the fine pores, and any amount supported inside the fine pores is minimal.

The method described in Patent Literature 3 is one whereby AC voltage is applied, in a metallic salt solution, to the surface of an aluminum material on which an anodized film has been formed, to achieve coloring; however, anodization treatment is given only once and the depositing of a metallic compound inside the fine pores is not suggested.

Also regarding the method described in Patent Literature 4 whereby a pigment is filled in fine pores formed by an anodized film, there is a step to etch the anodized film to dissolve the barrier layer before the pigment is filled, and, needless to say, this etching step is incapable of dissolving only the barrier layer inside the fine pores and clearly the entire anodized film is etched. As a result, an irregular surface is formed over the entire anodized film, and even if color is added, the formed aluminum sheet will have an irregular, non-uniform surface at best.

In addition, etching the formed anodized film means that the anodized film is lost. Therefore, although there are fine pores, the interior of the fine pores is not protected by the anodized film and, as the aluminum material is used over time, the interior of the fine pores and surface of the aluminum material will corrode.

Accordingly, an object of the present invention is to obtain a shaped aluminum article which has an opaque and sufficiently colored film produced by filling grains of titanium dioxide or other pigment into fine pores formed by means of anodization, maintains its original shape, and provides the inherent physical properties of the anodized film.

Means for Solving the Problems

The inventors of the present invention studied in earnest to achieve the aforementioned object and invented the shaped aluminum article and method of manufacturing such shaped aluminum article as described below:

1. A shaped aluminum article having an anodized film formed on its surface, where a pigment is filled in fine pores formed on the anodized film at a density of 2 mg to 30 mg per 1 square decimeter. 2. A shaped aluminum article according to 1, wherein the diameters of the openings of the fine pores are 50 to 300 nm. 3. A shaped aluminum article according to 1 or 2, wherein the lengths of the fine pores in the depth direction of the shaped article are 5 to 50 μm. 4. A shaped aluminum article according to any one of 1 to 3, wherein the anodized film on the surface of the shaped aluminum article has been formed using a method that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage. 5. A method of coloring the surface of shaped aluminum article, whereby an shaped aluminum article is given an anodization treatment that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage, which is followed by a process of filling a pigment in the fine pores that have been formed. 6. A method of coloring the surface of shaped aluminum article according to 5, wherein the process of filling a pigment is an electrophoretic migration process using a pigment dispersion liquid and/or pigment sol-containing liquid.

Effects of the Invention

Compared to the conventional painting method, according to the present invention, the colored film is not removed unless the anodized film peels. In addition, the shaped aluminum article that has been colored by a pigment introduced into the fine pores of the anodized film exhibits an especially deep color in a stable manner because more pigment can be fixed. Moreover, sufficient coloring can be achieved even when a pigment whose primary grain size is too small for the pigment color to be exhibited is used, because secondary aggregation can be achieved inside the fine pores.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A schematic view of the step in which titanium oxide grains are introduced under the present invention.

FIG. 2 A graph showing the relationship of the current and time of electrophoretic migration.

FIG. 3 Analysis photographs and graph of the colored shaped aluminum article proposed by the present invention.

MODE FOR CARRYING OUT THE INVENTION

The present invention can be implemented by filling pigment grains that are dispersed in a solvent, in fine pores formed on an anodized film. In addition, even when grains of titanium oxide, etc., are used whose grain size is smaller to a point where the primary grains are too small to normally exhibit a white color, for example, use of a dispersion liquid in which these grains in solated state are dispersed allows these pigment sol grains to aggregate and form aggregated grains inside the fine pores, and this results in the light entering from the outside reflecting diffusely between the titanium oxide grains constituting these aggregated grains to increase the opacity, which in turn causes the aggregated titanium oxide grains to exhibit a white color and consequently the anodized film exhibits a white color. The same can be said with other pigments, not just titanium oxide.

Therefore, when the openings of the fine pores in the anodized film are sufficiently large, and when titanium oxide grains or grains of other pigments, or aggregated grains formed therefrom, for example, which already have the coloring ability as a white pigment, are introduced through these openings, thereby causing the film to exhibit a white color as a result, then an anodized film more densely colored compared to the shaped aluminum article can be obtained.

Such shaped aluminum article proposed by the present invention is manufactured through the fine pore formation step based on two-stage anodization, and the subsequent pigment filling step, as described below.

One commonality of any method conforming hereto is that a pigment or sol is introduced into fine pores that have been obtained by means of anodization treatment in a target which is a shaped aluminum article.

The anodization method used under the present invention is one which is applied to shaped articles made of the aluminum materials described below.

(Aluminum Material for Shaped Aluminum Article)

The aluminum material constituting the shaped aluminum article proposed by the present invention may be made only of aluminum, but it can also be made of any so-called aluminum alloy (such as Al—Mn alloy, Al—Mg alloy, Al—Mg—Si alloy, etc.), so long as fine pores will be formed through anodization treatment. In addition, any material which is made by alloying aluminum material with other metal and thus is already colored, can also be used.

Which aluminum material should be used is determined according to the application of the shaped aluminum article proposed by the present invention.

Pigments that can be used under the present invention include any known pigments, and titanium oxide, iron oxide, carbon black, zinc oxide, copper phthalocyanine blue, copper phthalocyanine green, azo compound, quinacridone compound, anthraquinone compound, diketopyrrolopyrrole compound, perylene compound, perynone compound, dioxazine compound, derivative thereof, or the like can be used, and a pigment that can be contained in the treatment solution used in the anodization treatment steps can be selected.

In terms of grain size, any pigment having a known grain size in a range associated with a usable coloring pigment can be adopted, but pigments whose grain size are no more than 100 nm or so may be used. If the grain size exceeds 100 nm, filling the pigment in the fine pores becomes difficult.

Also, as to which sol can be used under the present invention, any sol made of a material that can be used as the aforementioned pigment can be adopted.

[Fine Pore Formation Step]

The fine pore formation step based on two-stage anodization is described.

(Two-Stage Anodization Method) (First Anodization Treatment)

The first stage of anodization treatment to obtain the shaped aluminum article proposed by the present invention is a treatment to form an anodized film on the surface of a shaped aluminum article to add corrosion resistance and decorativeness to the surface, and it must be able to form fine pores on the anodized film.

A shaped aluminum article is soaked in an electrolytic solution together with the anode and cathode of an anodization treatment apparatus in such a way that it is electrically contacting the anode, and by supplying power between the anode and cathode, an anodized film is formed on the shaped aluminum article.

For the electrolytic solution used here, preferably an electrolytic solution containing an organic acid, such as one containing phosphoric acid like a mixture of oxalic acid and phosphoric acid, mixture of malonic acid and phosphoric acid, mixture of maleic acid and phosphoric acid, etc., can be used; however, it is not limited to the foregoing. However, a mixture of maleic acid and phosphoric acid is preferable, for example.

The first stage of anodization is implemented under a condition of maintaining a constant current density. Preferably the current density here is 0.5 to 2.0 A/dm². As such treatment progresses, the voltage will become constant after reaching a certain level, after which the treatment will be continued, if desired, for a specified time at this constant current and constant voltage.

The fine pores that generate are formed as fine pores 3 that are long columnar voids extending in the depth direction of the anodized film 2 formed on the surface of the shaped aluminum article 1, as shown in FIG. 1 (a), for example. However, they are not necessarily formed at right angles to the surface of the shaped aluminum article as illustrated; instead, they actually assume a bent, branched, or other irregular shape. The diameters of their openings can be adjusted as desired according to the anodization conditions, but under the present invention, the fine pores of the anodized film generated in this step have an opening diameter of 50 to 300 nm, or preferably 100 to 250 nm. If the opening diameter is larger than 300 nm, obtaining a uniform anodized film becomes difficult; if it is less than 50 nm, on the other hand, depositing a sufficient amount of titanium oxide grains or other pigment grains inside the fine pores becomes difficult.

Also, the lengths of fine pores are not limited in any way; to deposit the amount of pigment needed to ensure sufficient coloring by the pigment, however, the fine pores are 5 to 50 μm long, or preferably 10 to 40 μm long, from the aluminum surface in the thickness direction.

(Second Anodization Treatment)

In the second stage, anodization is implemented by changing the applied voltage. Here, the voltage is changed by causing it to drop in steps at pre-determined intervals and/or intervals to achieve pre-determined currents. When the higher bath voltage E1 is changed to the lower bath voltage E2 during the electrolysis, the current becomes virtually zero for a moment, and then gradually rises and eventually reaches a steady-state level appropriate for E2. In other words, the thickness of the barrier layer is proportional to the voltage. Immediately after the change to E2, the barrier layer becomes thin, despite the current being zero, because the barrier layer is dissolved in the electrolytic solution, and as a steady-state current is eventually reached, the electrolytic reaction progresses.

By changing the voltage and repeating the electrolytic reaction this way, the fine pore diameters can be increased while the thickness, primarily of the barrier layer, can be decreased.

The treatment solution in this step can be any known solution for anodization treatment that can be used in the first stage of anodization treatment, and the electrolytic solution used in the first stage can be used continuously.

[Pigment Filling Step] (Step to Attach Pigment to Interior Walls of Fine Pores)

Under the present invention, the step to deposit the pigment inside the fine pores of the anodized film is a step to cause electrophoretic migration of a pigment dispersion liquid and/or pigment sol relative to the anodized shaped aluminum article.

The pigment dispersion liquid used here is a water-based solvent containing a specified pigment, pigment dispersing resin, and in some cases, water-soluble organic solvent, and any known additive may be combined as necessary.

In this step, the pigment concentration in the pigment dispersion liquid is in a range of 0.1 to 10.0 percent by weight, and if this range is deviated from, the pigment may not be filled sufficiently or its dispersibility may drop.

Also, if a dispersion liquid of titanium oxide is used, for example, its pH is adjusted to 8.0 or more, or preferably between 9.0 and 11.0.

By causing the titanium oxide grains to deposit inside the fine pores, the pigment 4 deposits inside the fine pores 3, as shown in FIG. 1 (b).

The pigment, as mentioned here, is desirably constituted by primary grains or secondary grains. Their average grain size (D50) is preferably 5 to 100 nm. If the average grain size exceeds 100 nm, it becomes difficult to introduce the pigment into the fine pores formed on the anodized film, through the openings of the fine pores; on the other hand, it is difficult to find a pigment whose primary grain size is less than 5 nm.

Examples of the dispersion agent or other water-soluble resin contained in the pigment dispersion liquid include: polyvinyl alcohol resin, gelatin, polyethylene oxide, polyvinyl pyrrolidone, acrylic resin, styrene-acrylic resin, acryl amide resin, urethane resin, dextran, dextrin, carrageenan κ, τ, λ, etc.), agar, pullulan, water-soluble polyvinyl butyral, hydroxy ethyl cellulose, carboxy methyl cellulose, etc., epoxy resin, polyimide resin, polyamide resin, cellulose resin, polyester resin, or the like.

The content of the water-soluble resin is preferably 1 to 30 percent by weight relative to 100 percent by weight of the entire dispersion liquid in which the pigment is dispersed.

It should be noted that, under a method where a pigment sol is used, use of the aforementioned water-soluble resin is not necessarily required.

The water-soluble organic solvent contained in the dispersion liquid may be, for example, alcohol (such as methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), polyalcohol (such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexane diol, pentane diol, glycerin, hexane triol, thiodiglycol, etc.), polyalcohol ether (such as ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monomethyl ether, diethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, propylene glycol monophenyl ether, etc.), amine (such as ethanol amine, diethanol amine, triethanol amine, N-methyl diethanol amine, N-ethyl diethanol amine, triethyl amine, morpholine, N-ethyl morpholine, ethylene diamine, diethylene diamine, triethylene tetramine, tetraethylene pentamine, polyethylene imine, pentamethyl diethylene triamine, tetramethyl propylene diamine, etc.), amide (such as formamide, N,N-dimethyl formamide, N,N-dimethyl acetoamide, etc.), heterocycle (such as 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, etc.), sulfoxide (such as dimethyl sulfoxide, etc.), sulfone (such as sulfolane, etc.), urea, acetonitrile, acetone, etc. Preferable water-soluble organic solvents include polyalcohols such as ethylene glycol. In addition, polyalcohol and polyalcohol ether may be combined.

The content of this water-soluble organic solvent is preferably 0 to 40 percent by weight relative to 100 percent by weight of the dispersion liquid in which the pigment is dispersed.

If a pigment sol is used, any known inorganic compound sol can be used which, when aggregated, becomes a pigment and allows a colored shaped aluminum article to be obtained.

For such sol, a colloidal titanium oxide sol, zinc oxide sol, iron oxide sol, copper oxide sol, or other inorganic compound sol that can serve as a pigment can be used, for example.

Any pigment sol whose grains are approx. 5 to 100 nm in size can be adopted.

As for the conditions of electrophoretic migration using a pigment dispersion liquid or pigment sol, an shaped aluminum article on which fine pores have been formed is set in a dispersion liquid or sol of room temperature, and the voltage is raised at a rate of 0.5 to 2V per second and kept at 50 to 200V for 30 seconds to 5 minutes. During that time, water is electrolyzed inside the fine pores and the generated hydrogen ions cause the pigment dispersion body or sol to aggregate and become insoluble, thereby filling the fine pores with the pigment.

Or, preferably the shaped aluminum article is soaked further for 1 to 10 minutes in an aqueous solution of 20 to 70° C. containing maleic acid or other weak acid by 0.1 to 2.0 percent by weight, so that the shaped aluminum article can be neutralized and the dispersion body in the fine pores can be fixed.

Once the pigment is filled in the fine pores by means of electrophoretic migration using the pigment dispersion liquid and/or pigment sol as described above, the pigment may attach to parts of the surface of the shaped aluminum article that are not fine pores, in which case the pigment attached outside the fine pores can be removed by washing it using triethanol amine, water, etc. By removing the pigment this way, a possibility that so-called “over-deposition” occurs and makes it difficult to add a vivid color, is eliminated.

On the shaped aluminum article formed according to the present invention, the pigment filled in the fine pores, if it is a metallic compound, has a metal content ranging from 2 to 30 mg/dm² per 1 dm² (square decimeter) of its surface. By filling the pigment at a density such as 2 to 30 mg/dm², the coloring strength can be improved further compared to when any conventional coloring method is used.

When a titanium oxide pigment is filled, for example, the surface color is clearly white, especially because the L* value is 78 or more and also the a* and b* values are both in a range of 0±5.

Furthermore, the shaped aluminum article proposed by the present invention need not be deglossed.

Such shaped aluminum article proposed by the present invention can be used in many fields and applications where shaped aluminum articles have been used. For example, it can be adopted in all applications relating to furniture, tableware, containers, home appliances, articles of daily use, etc., where a shaped aluminum article with a white surface is required.

Example 1 Method of Filling Pigment in Fine Pores by Causing Electrophoretic Migration of Pigment Dispersion Liquid

(Aluminum Sheet Anodization Treatment Step)

The anodization treatment step was implemented in the form of the first anodization treatment (constant-current anodization treatment) and second anodization treatment (constant-voltage anodization treatment) as described below

(First Anodization Treatment)

An electrolytic solution for forming anodized film, containing 30 g of 85% phosphoric acid and 30 g of maleic acid per 1 liter, was prepared.

This electrolytic solution for forming anodized film was adjusted to 30° C., and an aluminum sheet was soaked in it and anodized at a current density of 1.0 A·dm⁻² for an electrolysis time of 45 minutes. The final voltage in this anodization treatment step was approx. 120V.

(Second Anodization Treatment)

Subsequently, the second anodization treatment step, being a step to perform anodization treatment at a constant voltage, was performed by gradually lowering the constant voltage.

First, the voltage was lowered from 120V to 100V and fixed. The current, although low at first, gradually rose and became roughly constant, at which point the voltage was lowered to 80V and fixed in the same manner, thus causing the current to rise and become roughly constant. This step was repeated by lowering the voltage by 20V at a time, until the current rose to a constant level at the final voltage between 40V and 100V.

Although the thickness of barrier layer (thickness from the bottom of the fine pore to the surface of the aluminum sheet on the opposite side) varied depending on this final constant voltage, and the fine pore depth also varied as a result, extremely narrow and long fine pores of 19±1 μm in depth and 150 to 200 nm in diameter could be formed.

(Preparation of Pigment Dispersion Body, and Electrophoretic Migration Step)

As titanium oxide, 10 parts by weight of anatase-type titanium oxide powder of 6 nm in average primary grain size as obtained using a transmission-type electron microscope was adopted and dispersed in a solvent comprising triethanol amine and water, using 10 parts by weight of Joncryl 679 (acrylic co-polymer) manufactured by BASF as dispersion agent, to prepare a pigment dispersion liquid.

This dispersion liquid contained 0.6 percent by weight of the titanium oxide of 28 nm in grain size (D50% by volume as measured according to the dynamic light scattering method), as well as triethanol amine, with its pH adjusted to 8.3 or 9.5.

The aluminum sheet that had completed the first anodization treatment was given the second anodization treatment under the conditions shown in Table 1 below, after which it was put through the electrophoretic migration step in the pigment dispersion liquid. The obtained aluminum sheet thus treated was washed with an aqueous solution of triethanol amine to remove the titanium oxide attached outside the fine pores and thereby eliminate over-deposition.

TABLE 1 Final voltage Color difference from Amount of Pigment of second Migration voltage aluminum sheet surface titanium per dispersion anodization in electrophoretic before first anodization square decimeter liquid pH treatment migration step L* a* b* Interference treatment (ΔE) of surface (mg) 74.34 −1.51 −6.52 Yes 36.18 8.3 110 V 73.47 −2.48 −3.67 Yes 35.12 8.3 130 V 74.33 −2.27 −4.59 Yes 36.02 8.3 150 V 75.10 −1.65 −5.19 Yes 36.81 8.3 100 V  130 V 77.55 −1.70 −4.37 Yes 39.19 8.3 80 V 130 V 78.49 −2.12 −4.81 Yes 40.18 9.5 130 V 78.17 −1.50 −5.33 Yes 37.88 1.1 9.5 80 V 130 V 81.12 −1.23 −3.76 Yes 42.72 9.5 60 V 130 V 82.40 −0.95 −3.59 Virtually no 43.98 5.7 9.5 40 V 130 V 82.15 −0.63 −3.56 Virtually no 43.73 6.2 9.5 40 V 150 V 82.87 −0.66 −3.54 Virtually no 44.45

The method used to measure the amount of titanium per square decimeter of surface, shown in Table 1 above and Table 2 below, is as follows.

A solution was prepared by mixing and dissolving 35 ml of 85% phosphoric acid and 20 g of chromic acid anhydride in 1 L of ion exchanged water, from which 50 ml was taken, and the aluminum sheet of 20 mm×30 mm in size that had completed the electrophoretic migration treatment was soaked in this solution to let its film part dissolve at 50 to 100° C. At that point, the dissolved film component, and some titanium oxide grains that had been present in the film component, were present in the solution. Accordingly, the solution was heated after adding an appropriate amount of concentrated sulfuric acid (approx. 10 ml) to dissolve the titanium oxide. This solution was adjusted to a total volume of 100 ml, and the amount of titanium in the solution was quantified using an ICP-AES (inductively coupled plasma atomic emission spectroscope).

L*, a* and b* shown in Table 1 above and Table 2 below were measured using the spectrophotometer SE2000 manufactured by Nippon Denshoku Industries, and interference was checked by visually checking the treated aluminum sheet to see whether or not an interference color would generate.

According to the results in the table above, or specifically the amounts of titanium oxide filled as expressed by brightness L*, the surface-treated aluminum sheets conforming to the present invention, corresponding to three examples in the table, had a brightness L* of 82.15 or more and presented virtually no interference. Also, their a* value was −1.00 or more, and the b* values in these examples were −3.60 or more. It should be noted that, because these color characteristics are also affected by the color of the aluminum sheet which is the base material, the aforementioned ranges are limited to these examples.

In all of these three examples, the final voltage of second anodization treatment was 40V or 60V, which is a result based on the barrier layer being a thin film.

Also, the graph shown in FIG. 2 explains the different electrophoretic migration conditions applied, under each treatment condition used for the second anodization treatment, when the electrophoretic migration was performed on the colored aluminum sheets obtained using the method of filling the pigment in the fine pores by causing the pigment to migrate.

The graph line denoted by 1 in FIG. 2 represents an example where the second anodization treatment was not performed and the pH during the electrophoretic migration of pigment was 8.3, which is outside the scope of the present invention. Similarly, the graph line denoted by 2 represents an example where the second anodization treatment was performed for 15 minutes at 40V and the dispersion liquid had a pH of 8.3 during the electrophoretic migration, the graph line denoted by 3 represents an example where the second anodization treatment was performed for 15 minutes at 60V and the dispersion liquid had a pH of 9.5 during the electrophoretic migration, and the graph line denoted by 4 represents an example where the second anodization treatment was performed for 15 minutes at 40V and the dispersion liquid had a pH of 9.5 during the electrophoretic migration. All graph lines have a peak shortly after 120 seconds, but clearly the graph lines denoted by 2 to 4 indicate a longer electrophoretic migration time at a higher current density compared to the graph line denoted by 1. This means that, based on this graph, more pigment was filled in the fine pores in the examples denoted by 2 to 4, than the example denoted by 1.

Also, comparison of 2 and 3 finds that, while 2 should have allowed for treatment at a higher current density because of the lower voltage, the measured current density was lower because the pH was lower. It is clear from this result that the higher the pH value of the dispersion liquid during the electrophoretic migration, the better.

Example 2 Method of Filling Pigment in Fine Pores by Causing Electrophoretic Migration of Pigment Sol (Aluminum Sheet Anodization Treatment Step)

As for the method for anodization treatment of aluminum sheet, the method employed in Example 1 above was adopted.

The pigment sol solution used for electrophoretic migration was prepared by adjusting the pH of a peptized titanium oxide sol (containing 20 percent by weight of equivalent titanium oxide, 6 nm in primary average grain size, anastase type, neutral, solvent=water) by adding triethanol amine and triethyl amine and then diffusing the sol using a dispersion machine.

The titanium oxide concentration in the pigment sol solution was 0.5 percent by weight, and the electrophoretic migration conditions were the same as those in Example 1.

The only treatment given to the aluminum sheet after the titanium oxide pigment had been filled in the fine pores was washing it with water.

TABLE 2 Final voltage Migration Color difference from Amount of of second voltage in aluminum sheet surface titanium per Pigment sol anodization electrophoretic before first anodization square decimeter pH treatment migration step L* a* b* Interference treatment (ΔE) of surface (mg) 74.34 −1.51 −6.52 Yes 36.18 80 V 77.90 −1.54 −5.48 Yes 39.62 60 V 79.08 −1.67 −4.55 Yes 40.73 9.5 130 V 81.95 −1.56 −3.95 Yes 43.56 1.2 9.5 60 V 130 V 82.84 −1.67 −3.56 Virtually no 44.44 7.1 9.5 60 V 140 V 82.90 −1.90 −2.96 Virtually no 44.49 9.5 60 V 150 V 84.17 1.30 −2.55 Virtually no 45.99 10.7 40 V 79.66 −1.58 −4.41 Yes 41.30 9.5 40 V 150 V 81.55 −0.91 −4.09 No 43.15 9.5 40 V 180 V 82.13 −0.68 −3.6 No 43.71 9.5★ 40 V 150 V 80.14 −0.62 −3.23 No 27.57 9.5★★ 40 V 160 V 81.27 −2.01 −3.48 No 37.68 9.5* 20 V 160 V 81.21 −0.75 −4.98 No 42.86 10.5⋆ 60 V 130 V 81.09 −0.53 −3.88 No 42.68

Checking the results in Table 2 finds that, when the final voltages of second anodization treatment ranged from 20 to 60V and the electrophoretic migration step was performed, there was little or no interference on the surface of the obtained aluminum sheet that had been treated, and furthermore the amounts of titanium oxide, or the white pigment filled in the fine pores, are 80.00 or more in brightness L*, with the range of a* being −1.60 or more and that of b* being −5.00 or more.

Now, an aluminum sheet made of 6063 alloy (Al—Mg—Si type) was used in the example denoted by 9.5 (★) in the Pigment dispersion liquid pH field. An aluminum sheet made of 6061 alloy (Al—Mg—Si type) was used in the example denoted by 9.5 (★) in the Pigment dispersion liquid pH field. In other examples, a sheet made of pure aluminum for industrial use was used. Since the base aluminum material was different and the color of base material also differed, the values of L*, a* and b* are slightly different in these examples compared to the examples two rows above which were produced under the same conditions except for aluminum sheet materials.

FIG. 3 (a) shows a SEM image, FIG. 3 (b) shows a titanium atom mapping image based on EDX imaging analysis of film surface, and FIG. 3 (c) shows a titanium atom mapping image of a section based on EDX imaging analysis, of the treated aluminum sheet corresponding to the example denoted by 10.5 (⋆) in the pH field in Table 2. Furthermore, FIG. 3 (d) shows the analysis results of rf-GD-OES (radio frequency glow discharge optical emission spectroscopy), revealing the locations of titanium atoms, oxygen atoms and aluminum atoms in the depth direction of the aluminum sheet.

The fine pores formed on the surface of the aluminum sheet by anodization treatment can be observed in the image of FIG. 3 (a). It is clear that these fine pores have roughly the same diameter and are formed uniformly.

Furthermore, it is clear from looking at FIG. 3 (b) that titanium atoms indicated by white dots are present, or specifically the pigment of titanium oxide is present, at the fine pores observed in FIG. 3 (a).

In addition, FIG. 3 (c) shows that the surface of the aluminum sheet corresponds to the region in the top section of this image populated by some titanium atoms indicated by bright dots, and that a band-shaped area exists below it in the image where bright dots indicating titanium atoms are concentrated, and this band-shaped area is the very evidence that the pigment of titanium oxide is present at the bottom of the fine pores.

FIG. 3 (d) illustrates this trend using a different set of results. This graph, created by sputtering the treated aluminum sheet and concurrently checking the types of atoms detected, measures atoms present at deeper locations, as time elapses further, from the surface of the treated aluminum sheet corresponding to the point of zero seconds of sputtering time. These results show that the titanium atom intensity has a peak of approx. 0.3 around 20 to 30 seconds of sputtering time, followed by another peak exceeding 0.5 at a point after 300 seconds, after which the intensity drops. By comparison, the oxygen atom intensity goes up and down within a range of approx. 1 to 1.5 until around 350 seconds after the start of sputtering, and weakens after 400 seconds.

Behaving completely differently from the oxygen intensity is the aluminum intensity which remains around 0.5 for 350 seconds or so and then increases suddenly thereafter. It should be noted that the titanium intensity is 500 times higher than the aluminum or oxygen intensity.

Putting these trends into perspective, it is found that, while titanium oxide is present on the surface, thereafter there is also a layer where the content of titanium oxide increases from the 250-second point to over the 350-second point or so.

When all that is indicated by these figures is put into perspective, it is clear that the treated aluminum sheets in the examples have many fine pores at their surface which are extending in the thickness direction, and that the titanium oxide pigment is filled deep in these fine pores.

As a result, the surfaces of these aluminum sheets have a color that strongly reflects the color of the titanium oxide pigment, or specifically a white color. Also, the surfaces of the obtained aluminum sheets were free from etching, and as this prevented deglossing, the obtained color was more vivid.

DESCRIPTION OF THE SYMBOLS

-   -   1 - - - Shaped aluminum article     -   2 - - - Anodized film     -   3 - - - Fine pore     -   4 - - - Titanium oxide grain 

1. A shaped aluminum article having an anodized film formed on a surface, where a pigment is filled in fine pores formed on the anodized film at a density of 2 mg to 30 mg per 1 square decimeter.
 2. A shaped aluminum article according to claim 1, wherein a diameter of an opening of the fine pore is 50 to 300 nm.
 3. A shaped aluminum article according to claim 1, wherein a length of the fine pore in a depth direction of the shaped article is 5 to 50 μm.
 4. A shaped aluminum article according to claim 1, wherein the anodized film on the surface of the shaped aluminum article has been formed using a method that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage.
 5. A method of coloring a surface of shaped aluminum article, whereby an shaped aluminum article is given an anodization treatment that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage, which is followed by a process of filling a pigment in fine pores that have been formed.
 6. A method of coloring a surface of shaped aluminum article according to claim 5, wherein the process of filling a pigment is an electrophoretic migration process using a pigment dispersion liquid and/or pigment sol-containing liquid.
 7. A shaped aluminum article according to claim 2, wherein a length of the fine pore in a depth direction of the shaped article is 5 to 50 μm.
 8. A shaped aluminum article according to claim 2, wherein the anodized film on the surface of the shaped aluminum article has been formed using a method that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage.
 9. A shaped aluminum article according to claim 3, wherein the anodized film on the surface of the shaped aluminum article has been formed using a method that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage.
 10. A shaped aluminum article according to claim 7, wherein the anodized film on the surface of the shaped aluminum article has been formed using a method that includes an anodization treatment stage implemented under a condition of constant current, and a subsequent anodization treatment stage implemented at a constant voltage. 